-LRB- CNN -RRB- -- Women undergoing in-vitro fertilization should have only one or two embryos transferred during the process , depending on their age , says a study published Wednesday in the British medical journal The Lancet . Transferring three or more embryos during any IVF cycle should be avoided when possible , researchers say .

The prospective study analyzed more than 124,000 IVF cycles that ultimately led to the birth of more than 33,000 babies from January 2003 to December 2007 . The data were obtained via the UK Human Fertilisation and Embryology Authority , a database of all fertility treatments conducted in the United Kingdom . The study excluded treatment cycles that transferred frozen embryos .

The researchers divided the women in to two groups : Women younger than 40 and those 40 and older . The study found that in women 40 and older , transferring more than one embryo resulted in a higher rate of live births . However , transferring three or more embryos in a single cycle also led to a higher rate of health complications for both the mother and the baby , in part because the chance of giving birth to twins or triplets was higher .

These two findings led authors to conclude that women who are 40 and older should have two embryos transferred per IVF cycle , while younger women should have only one embryo transferred , and no patients should have more than three embryos transferred at one time .

`` We show that even in older women , we should never have more than three embryos transferred , '' says Scott Nelson , one of the study authors who is a professor of reproductive and maternal medicine at the University of Glasgow .

`` It does n't improve the chances of a woman having a healthy baby . ''

Dr. Glenn Schattman is a reproductive endocrinologist and the president of the Society for Assisted Reproductive Technologies -LRB- SART -RRB- . He agrees that maximizing the chance of a healthy pregnancy while at the same time limiting the chance for multiple births should be the ultimate goal of reproductive clinicians . However he disagrees with the study 's interpretation .

`` There are limitations of the study that concern me significantly in terms of the conclusions that were drawn , '' says Schattman .

In the United States , unlike the United Kingdom , transferring three embryos is more of an acceptable practice if certain prognostic indicators are present .

According to Schattman , a woman 's age is the most important factor in terms of pregnancy outcome but needs to be looked as a continuous variable . He says one major limitation of Nelson 's study is that the women were lumped in to only two groups : those younger than 40 and then the rest , when in reality the chances of a woman getting pregnant can depend on other variables as well .

`` We look at women under the age of 35 , 35 to 37 , 38 to 39 , '' and so on , says Schattman .

He says transferring three embryos is a valid practice if certain factors are in play , including a woman 's age , the number of failed IVF cycles she has already experienced and the quality of her embryo .

`` If you limit the number of embryos you put back inside of a 42-year-old woman , you reduce her chance of having a child , '' because implantation rates are so low for a woman that age , says Schattman .

Conversely , according to the 2009 embryo transfer guidelines published by SART , a 37-year-old woman could receive three embryos if she had already experienced failed IVF attempts or had poor quality embryos .

So what 's the bottom line for women considering IVF ?

Because IVF is an involved , often draining , process , Schattman says doctors need to determine how many embryos will be transferred on a case by case basis .

`` We ca n't set an absolute limit that applies to every person , '' says Schattman .

`` Twins are not an ideal outcome and not a desired outcome . You really want to adjust the number of embryos ... to not only maximize the chance of achieving a pregnancy but to counter that with a desire to reduce multiple births . ''

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Study published in Lancet analyzed more than 124,000 in-vitro fertilization cycles

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It discourages transferring three or more embryos during any IVF cycle

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One expert disagrees : `` There are limitations of the study that concern me ''